1. Field of the Invention
The present invention relates to active sensor circuits, and in particular, to active sensor circuits required to operate at low power and low duty cycle.
2. Description of the Related Art
With recent advancements in semiconductor manufacturing and sensor technologies, low power sensor networks, particularly those operating wirelessly, are providing new capabilities for monitoring various environments and controlling various processes associated with or within such environments. Applications, both civil and military, include transportation, manufacturing, biomedical, environmental management, and safety and security systems.
Particularly for wireless sensor networks, low power operation is critical to allow for maximum flexibility and minimum form factor. It has been found that typical wireless sensor assemblies use upwards of 90% of their power merely on environmental or channel monitoring while waiting for the anticipated event(s) to occur. In other words, simply monitoring for the occurrence of an anticipated event requires the expenditure of nearly all available power. This is particularly true for acoustic sensors, which often require significant amounts of power.
This problem has been addressed thus far by having a low power, or “sleep,” mode of operation in which the back end of the sensor assembly, e.g., the signal transmitter, or “radio,” circuitry, is effectively shut down pending receipt of a signal indicating the occurrence of the anticipated event (e.g., a change in the local environmental conditions, such as acoustic noise or temperature). This can reduce power consumption of the sensor assembly to levels in the range of 10 to 50 percent of normal, or full power, operation. However, for a low duty cycle system where each sensor assembly may only spend a very small amount of time (e.g., 1%) performing data transmission, the power being consumed during such an idle period can still constitute a major portion of the overall power budget.